The present invention deals with packages, and is directed more specifically to a heat-sealable package blank, or package in semifinished form, particularly well suited for enclosing a video tape cassette or other commodity likely to be damaged by heat used in the fabrication of the package from the package blank.
Video tape cassettes for the recording and replay of television programs are normally housed in generally boxlike, forwardly opening packages for protecting the video tape cassettes and, for carrying identification legends and other markings, making the packages more aesthetically appealing to the consumer. The manufacture of such packages starts with the blanking of a relatively stiff sheet, as of paperboard or plastic material, into a desired shape complete with indented folding lines. The thus prepared blanks are then folded up into a boxlike shape, and the flaps are glued or otherwise united together to complete the desired packages. Video tape cassettes are inserted in these packages and, further enveloped in outer coverings, for shipping to the consuming market.
An objection to the above conventional packaging practice is that tape cassettes are inserted into the completed packages. The completed packages are, of course, far more bulky than the package blanks and so present a serious problem in storage and transportation. The insertion of tape cassettes into the packages is also in itself a trouble, taking much time as the packages may not necessarily be dimensioned to fit the cassettes.
It has been known to use sheets of thermoplastic material such as polypropylene, polyethylene or polystyrene, or composite sheets having facings of such thermoplastic material on both sides of a core of paper or the like. In the fabrication of video tape cassette packages from such thermoplastic sheets, the superposed flaps are fused together by heat and pressure or by known ultrasonic or high frequency welding techniques. In either case, however, the fusion of the flaps requires the insertion of bearing plates in the packages, making it impossible to form the packages with the cassettes prereceived therein. This known method limits the amount of packages produced from blanks to only thirty or so packages per minute.
Another known method uses heated air to unite the superposed flaps of the package blanks, in order to dispense with the need for bearing plates and hence make possible the manufacture of the packages with the cassettes prereceived therein. The heated air melts only the opposed surfaces of the superposed flaps, so that they can be fused together when lightly pressed against each other.
Although well calculated to increase the production of packaged cassettes, this known method has hitherto been impracticable by reason of the conventional design of the package blanks. As heretofore designed, the package blanks when folded into the approximate shape of packages, allowed heated air, to intrude into the packages, subsequently thermally deforming and otherwise impairing; consequent thermal deformation and other impairment of the tape cassettes housed in the package. This drawback of the prior art package blanks will be later discussed in further detail.